1. Field of the Invention
The present invention relates to improved multi-cellular foamed elements of thermoplastic or thermosetting resin based compounds such as for example, phenolic aldehyde resin based compositions, sandwiched between corrugated material. More particularly, the instant invention relates to improved sandwich-like composites comprising a core of foamed material such as a phenol formaldehyde resin compound sandwiched between and adhering to corrugated paper skins, said paper containing perforations made prior to the foaming of the foamable resin and the composite board being post-perforated after foaming the resin based compound between the two skins. The roof heat-insulating composite boards meet mechanical and heat insulating performance requirements at lower foam densities than similar composite materials with straight skins. At the same time the level of curling under conditions of one sided heating, e.g., during construction of a built-up roof, is reduced compared with other more incompressible skin composites. These roof insulating boards, when installed in built up roofs reduce the tendency of membrane blistering in conditions of large temperature changes, e.g., day and nightime.
2. Description of the Prior Art
The insulating properties of foamed plastic materials are well known. Indeed, a most frequently cited advantage of foamed resins, is their very low thermal conductivity. For example, the low thermal conductivity of foamed thermoset phenol formaldehyde materials causes them to be useful as insulating boards used in building structures such as partition walls, bulk heads, ceilings, floors, storage tanks, walls and roof structures.
When employed in roof structures, the insulating material must have sufficient strength to support bituminized roofing felt, asphalt, gravel and the like. More particularly, the boards should have sufficient strength to support the weight of a person or persons that may be required to work on the roof during the laying down of the bituminized roofing felt, asphalt, gravel and the like or person or persons that from time to time may be required on the completed roof. Typically, for phenolic foam composites sandwiched between skins, such as paper, the density is about 1.5 to about 4.5 lb./ft.sup.3 thereby having the strength to support such persons and their equipment.
The phenol formaldehyde resin based foamed material can be sandwiched between protective skins of paper, such as wood fiber based felt or creped kraft paper. With a reduction in the density of the foam, the rigidity and strength of the protective skins must necessarily be increased in order to support and distribute a load that may be placed upon the insulating board. If felt skin is used to protect the foam, curling becomes a problem. Curling occurs because the moisture which is present or absorbed in the foam, travels from the hot side of the board to the cool side of the board upon exposure of the board to the sun during the roofing operation.
In order to overcome the curling problem, it has been suggested that creped kraft paper be substituted for wood fiber felt paper.
This type of composite insulation board however, if installed in a built up roof system tightly enclosed between a flat support covered with a vapour retarder and the overlying roofing membrane, allows no fast relief for the pressure that can build up by the expansion of air and/or water vapour between the board and the roofing membrane during periods of high temperature exposure. This results in the blistering of the membrane leading to eventual membrane failure and roof leaks.
The advantage of the corrugated skin composite insulating board is that the equilibration of the pressure in a built up roof is enhanced in such conditions by the presence of the corrugated flutes which act as pressure equilibration channels.
Therefore it is particularly desirable to provide a roof-insulating board which has strong skins thereby allowing for the reduction of the foam density employed between the skin while maintaining the required mechanical and thermal insulating properties of the board. It is particularly desirable to provide a roof insulating board which manifests reduced curling under the heat of the sun. In addition, it is particularly desirable to provide a roof insulating board which diminishes the tendency of tightly built up roof systems to blister under conditions where pressure builds up due to high temperatures. It is also desirable to provide a roof insulating board which has a high mechanical strength in conditions of high humidity in built up roof systems, thus resisting the uplift produced by high winds.
U.S. Pat. No. 2,973,295 of Rodgers, Jr. issued Feb. 28, 1961 describes a process for incorporating foamable materials in corrugated paperboard. U.S. Pat. No. 3,821,337 of Bunclark et al describes a process for controlled curing of foams such as foamed phenol-aldehydes employed in insulating boards. U.S. Pat. No. 3,536,575 of Maitrot issued Oct. 27, 1970 describes a method of producing sandwich like heat-insulating boards. U.S. Pat. Nos. 3,741,920 issued June 25, 1973 and 3,726,708 issued Apr. 10, 1973 each assigned to Dynamit Nobel Atktiengesellschaft describe phenolic resin foams which may be used as the core material in the manufacture of heat-insulating board. U.S. Pat. Nos. 3,694,387 of Junger et al issued Sept. 26, 1972, 3,779,956 of Pintin et al issued Dec. 18, 1973, 3,877,967 of Junger et al issued Apr. 15, 1975 and 3,953,645 of Moss issued Apr. 22, 1976 each describe phenolic resins which can be employed in the manufacture of heat-insulating board.